Circuits and methods of driving laser diodes (LD) such as vertical cavity surface emitting laser (VCSEL) diodes are known. Furthermore it is known that these circuits facilitate an efficient manner of producing lasing optical output power, primarily in the form of a pulse shape (commonly referred to as a pulsed train), but may also be in the form of an arbitrary waveform (such as a sine wave). These arbitrary waveforms may be defined by a continuous wave (CW) input.
The ability to drive the laser diode to generate a suitable continuous wave light intensity output has many applications. For example, generating a continuous wave light intensity output enables the laser diode to encode information for transmission within the optical output signal as well as enabling timed event detection.
Laser diode current supplies or current drivers produce an output which produces a signal or pulse shape having a defined rise time (Tr) and fall time (Tf). This rise and fall time defines a limit for pulse width and similarly for bandwidth of signaling. The rise and fall times of conventional laser diode current drivers is defined by the parasitic transistor capacitances within the circuits and the ability for the capacitances to charge/discharge based on the circuit arrangement.
Furthermore there are no conventional pulse current drivers which are able to feature arbitrary waveform generation by manner of a digital input and thus via a digital-to-analog (D/A) translation.
A further issue with conventional current drivers is one of driving current to the laser diode within the diode's linear range and furthermore being able to do so within the limitation of the driver circuit topology and supply voltage headroom.
Conventional laser diode driver circuit topology attempts to maintain that the laser diode current remains invariant to varying supply voltage levels, but limitations exist where, for levels in which the headroom limit is exceed, the laser diode output current range is no longer linear. This produces the effect of a tapering down of peak current. Furthermore this prevents linear granularity of control in output optical power and furthermore reproduction (D/A) of distortion free waveforms.